Leases - Components of lease expense (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating lease cost
Operating lease cost	$ 44.1	$ 47.5
Finance lease cost
Amortization of right-of-use assets	4.1	2.5
Interest on lease liabilities	0.5	0.8
Variable lease cost	8.1	9.2
Total lease cost	$ 56.8	$ 60.0